Inhibiting corrosion in aqueous films

ABSTRACT

In a process for the exploration for or the production of crude oil and/or natural gas, wherein metal objects are exposed to a gas for period of time sufficient to produce an aqueous film, a method including introducing a corrosion inhibitor into a fluid in contact with the subject metal under conditions sufficient to introduce the corrosion inhibitor into the aqueous film can be used to prevent excessive corrosion. Useful as the corrosion inhibitor is 2-sulfanylpropan-1-ol, also known as 2-mercapto-ethanol, and 2-mercapto-ethanol substituted with one or two methyl groups, and combinations thereof.

CROSS REFERENCE TO RELATED APPLICATIONS

The Application Claims priority from U.S. Provisional Patent ApplicationNo. 61/551,222 which was filed on Oct. 25, 2011 and which isincorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Disclosure

The invention relates to the prevention or mitigation of corrosion. Theinvention particularly relates to the prevention or mitigation ofcorrosion in aqueous films.

2. Background of the Disclosure

The problem of corrosion of metal surfaces in contact with air and wateris well known. Corrosion and pitting are accelerated in environments inwhich metal surfaces are in contact with corrosive chemicals such ashydrogen sulfide, carbon dioxide and organic acids, and water having ahigh electrolyte concentration. Such environments are typical ofdownwell conditions in oil and gas wells, in which corrosion of metalpipes, pumps and other equipment poses a serious problem requiringmonitoring of well sites, frequent maintenance and costly replacement ofparts.

Oil recovery operations in deep-sea oil fields present these corrosionproblems in their most extreme form. The downhole metal surfaces are incontact with large quantities of corrosive chemicals such as dissolvedacid gases present in the recovered oil, and the metal surfaces aresubjected to temperatures of 90° C. or higher and pressures of 1000 psigor higher, the extreme conditions of temperature and pressure acting toaccelerate corrosion and to intensify the problems of applying andmaintaining chemical protection for the equipment. Flow lines thatfollow the contours of the sea floor often have highpoints whereentrapped gas prevent the contact of liquids passing through the flowlines to contact at least parts of the top of the flowline.

Corrosion inhibition is particularly difficult when dealing withmultiphase fluids. For example, in gas wells, the exposed metal surfacesare often contacted for long periods with hydrocarbon gasses saturatedwith water. The application of corrosion inhibitors is difficult inthese situations. When conditions such as temperature and pressureinside such equipment favors the formation of aqueous films, theresulting aqueous films may selectively absorb or extract hydrophiliccompounds, many of which are corrosive, such as carbon dioxide andhydrogen sulfide.

SUMMARY

In one aspect, the invention is a method for employing a corrosioninhibitor to prevent or mitigate corrosion of metal in an aqueous film.

In another aspect, the invention is, in a process for the explorationfor or the production of crude oil and/or natural gas, wherein metalobjects are exposed to a gas for period of time sufficient to produce anaqueous film, introducing a vaporous corrosion inhibitor underconditions sufficient to treat the aqueous film with the vaporouscorrosion inhibitor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph illustrating the effect of various chemical on watercondensation; and

FIG. 2 is a graph of the Frequency changes that occur with an ironcoated quartz crystal when a water film is condensed in a system thatcontains 100 psi carbon dioxide.

DESCRIPTION

In one embodiment, the disclosure is directed a method for employing acorrosion inhibitor to prevent or mitigate corrosion of metal in anaqueous film. The corrosion inhibitors useful with method of thedisclosure include those selected from the group consisting of:

and combinations thereof.

In another embodiment, the invention is, in a process for theexploration for or the production of crude oil and/or natural gas,wherein metal objects are exposed to a gas for period of time sufficientto produce an aqueous film. In most embodiments, the aqueous film iscondensed from water vapor in the gas. In other embodiments, the filmmay also be the film resulting from a flush or surge of a liquid havingan aqueous component present. The method includes introducing acorrosion inhibitor under conditions sufficient to treat the aqueousfilm with the corrosion inhibitor. The compounds useful as the corrosioninhibitor include 2-sulfanylpropan-1-ol, also known as2-mercapto-ethanol, and 2-mercapto-ethanol substituted with one or twomethyl groups.

While not wishing to be bound by any theory, it is believed that thecorrosion inhibitors work by two processes. In a first process,surprisingly, these mercapto alcohols, despite their relatively lowmolecular weight, are effective at protecting a metal surface fromoxidation caused by acids. In a second process, it is believed thatthese same alcohols can retard the rate that water can condense into afilm on a metal surface. By reducing the volume of the fluid in the film(because the rate of condensation is lower), there is less fluid tosolubilize oxidation products and to adsorb corrosive compounds such ascarbon dioxide and/or hydrogen sulfide.

The methods of the disclosure may be used with any type of equipmentthat is subject to corrosion from a gas stream or phase. For example, inone embodiment, the method of the disclosure is used to protect thesurface of metal in contact with the production fluid from a gas well.For the purposes of this application, the production fluid from a gaswell includes the natural gas, minor amounts of readily condensablehydrocarbons, water, carbon dioxide, and other gases produced from thewell.

In such an embodiment, the corrosion inhibitors may be introduced as avapor or aerosol into a pipeline at a concentration sufficient to allowit to partition into the aqueous film. The concentration of corrosioninhibitor in the production fluid may vary as a function of thecomposition of the production fluid and can be determined by one ofordinary skill in the art of employing such additives, especially duringthe collection and transportation of natural gas.

Any equipment that may be exposed to a gas phase for a period sufficientto cause corrosion may be treated using the method of the disclosure.For example, flow lines, which for the purposes of this application arethe transfer lines used for offshore production that allow productionfluids to flow between oil and gas wells to reception points oftenfollow the contours of the sea floor. Where the flow line makes anabrupt bend, there is scope for a “bubble” to form where a liquid doesnot fully fill the flow line. In this gas space, also known as “the topof the pipe,” it is sometimes observed that excessive corrosion mayoccur.

This condition may be treated with the method of the disclosure wherethe corrosion inhibitor is introduced as a vapor or aerosol into thisgas space or, in an alternative embodiment, the corrosion inhibitor canbe selected such that it may be introduced into the production fluid andthen partition out of the liquid into the gas phase.

The corrosion inhibitors of the application may be introduced using anymethod known to those of ordinary skill in the art of exploring for orproducing oil and gas to be useful. The corrosion inhibitors desirablyhave a vapor pressure and solubility within the subject aqueous filmthat they easily and preferentially partition into the films.

Examples

The following examples are provided to illustrate the invention. Theexamples are not intended to limit the scope of the invention and theyshould not be so interpreted. Amounts are in weight parts or weightpercentages unless otherwise indicated.

Examples 1 & Comparative Examples A-CC

Corrosion tests were performed using 2-sulfanylethanol, diethyl amine,morpholine, and monoethyl amine. The corrosion tests were done in ahastealloy test apparatus where a quartz crystal microbalance was usedto measure corrosion rates. The use of this test apparatus is fullyexplained in the a publication: Cattanach, K., Jovancicevic, V.,Ramachandran and, R., and Sherik, A., “A New Methodology for MonitoringCorrosion under Sales Gas Conditions Using the Quartz CrystalMicrobalance”, Corrosion 11, Paper 1185 (Houston, Tex.: NACEInternational 2011).

In this study, the following chemicals were tested: volatile amines—S1)2-sulfanylethanol S2) diethyl amine (DEA), S3) monoethanol amine (MEA)and S4) morpholine (M). The total amount of fluid injected was a mixtureof 30 μl chemical and 250 μl distilled water that simulates the typicalconcentrations of inhibitors used in continuous applications.

Two types of tests were performed. In the experiments determining watercondensation rate in the absence and presence of various chemicals agold coated quartz crystal was used. A gold coated quartz crystal asreceived is used and placed in the vessel. The vessel is purged withnitrogen until a dew point temperature of −30° C. is attained. This stepremoves water from the system. The vessel is then pressurized and keptat temperature of 30° C. until a stable base line frequency is attained.Then 250 μl of solution are injected in the vessel. The frequency of thequartz crystal is monitored for thirty minutes and the crystaltemperature is cooled to 5° C. to induce condensation. As condensationoccurs, the frequency of the quartz crystal is reduced. When a stablecondensation layer is obtained, the crystal is heated back to 30° C. toremove the layer of condensation. If the frequency is essentially thesame as the frequency before the condensation, this indicates that thechanges in mass were due to condensation. See FIG. 2.

The effect of different chemicals on water condensation on gold coatedquartz crystal is shown in FIG. 1 which is a graph of the effects ofvarious chemical on water condensation. The crystal temperature is 5° C.The injected solution contains 30 μL of chemical and 250 μL of water. Itcan be seen from the graph that morpholine and proprietary alcoholexhibit significant effect on condensation rate and subsequent filmformation, while DEA and MEA had little/no affect on water condensation.The decrease in frequency occurs due to the formation of an aqueouscondensation layer.

In tests that measure the corrosion of iron and the effects of chemicalson the corrosion of iron, an iron coated quartz crystal is used. Theiron coated quartz crystal is placed in the vessel. The vessel is purgedwith nitrogen until a dew point temperature of −30° C. is attained. Thisstep removes water from the system. The vessel is then pressurized andkept at temperature of 30° C. until a stable base line frequency isattained. Than 250 μl of volatile corrosion inhibitor containingsolution are injected in the vessel. The frequency of the quartz crystalis monitored for thirty minutes and the crystal temperature is cooled to5° C. to induce condensation. As condensation occurs, the frequency ofthe quartz crystal is reduced. When a stable condensation layer isobtained, the crystal is heated back to 30° C. to remove the layer ofcondensation. At this point, the vessel is pressurized with 100 psi CO₂.The crystal temperature is then cooled to 5° C. to induce condensation.As condensation and corrosion occurs, the frequency of the quartzcrystal is reduced. The crystal is maintained at 5° C. for several hoursto allow for corrosion to occur. The crystal is then heated back to 30°C. to remove the condensation layer. At this stage the frequency changesof the quartz crystal microbalance are due to corrosion and theformation of a corrosion product layer.

The frequency drops were recorded and converted to a corrosion rate asdescribed previously. The results of the experiments are summarized inthe Table with experimentally determined as percent corrosioninhibition.

TABLE Corrosion Inhibitor Efficiency of Different Inhibitors SampleID/Inhibitor Corrosion Efficiency Ex. 1: 2-sulfanylethanol 80 Comp. Ex.A: diethyl amine 5 Comp. Ex. B: morpholine 22 Comp. Ex. C: monoethylamine 39

What is claimed is:
 1. A method for employing a corrosion inhibitor toprevent or mitigate corrosion of metal in an aqueous film.
 2. The methodof claim 1 wherein the corrosion inhibitor is selected from the groupconsisting of:

and combinations thereof.
 3. The method of claim 1 wherein the corrosioninhibitor is


4. The method of claim 1 wherein the corrosion inhibitor is


5. The method of claim 1 wherein the corrosion inhibitor is


6. The method of claim 1 wherein the corrosion inhibitor is


7. The method of claim 1 wherein the corrosion inhibitor functions tomitigate or prevent the formation of an aqueous film.
 8. The method ofclaim 1 wherein the metal is a surface within a gas well.
 9. The methodof claim 8 wherein production fluid with the gas well includes naturalgas, minor amounts of readily condensable hydrocarbons, water, andcarbon dioxide.
 10. The method of claim 1 wherein the metal is a surfacewithin a pipeline.
 11. The method of claim 1 wherein the metal is asurface within a flowline.
 12. The method of claim 11 wherein the metalis the top of the pipe within a flowline.
 13. The method of claim 12wherein the corrosion inhibitor is introduced as a vapor or aerosol intoa gas space within a flowline.
 14. The method of claim 9 wherein thecorrosion inhibitor is introduced into the production fluid and thenpartition out of the liquid into the gas phase.
 15. A process for theexploration for or the production of crude oil and/or natural gas,wherein metal objects are exposed to a gas for period of time sufficientto produce an aqueous film, introducing a vaporous corrosion inhibitorunder conditions sufficient to treat the aqueous film with the vaporouscorrosion inhibitor.
 16. The process of claim 15 wherein the corrosioninhibitor is selected from the group consisting of:

and combinations thereof.
 17. The method of claim 15 wherein thecorrosion inhibitor functions to mitigate or prevent the formation of anaqueous film.
 18. The method of claim 15 wherein the metal objects arein contact with a production fluid comprising natural gas, minor amountsof readily condensable hydrocarbons, water, and carbon dioxide.